Problem: What is the greatest common factor of $5$ and $45$ ? Another way to say this is: $\operatorname{gcf}(5, 45) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $5$ and $45$ The factors of $5$ are $1$ and $5$ The factors of $45$ are $1$ $3$ $5$ $9$ $15$ , and $45$ Thus, the greatest common factor of $5$ and $45$ is $5$. $\operatorname{gcf}(5, 45) = 5$